The patent and technical literature reflects significant on-going research and development effort targeting the advancement of coatings technology for use in industrial and architectural applications. Much research focus has been toward the development of water-based emulsion coatings as replacements for the traditional solvent-based coating formulations. Although water-based coatings suffer some disadvantages (they freeze in cold weather, corrode containers, support bacterial growth), their advantages, including reduced toxicity and reduced flammability and better adherence to damp substrates have encouraged their use for many high grade industrial and architectural finishes. Indeed, some of today's modern water-based emulsion type coating formulations can produce films having performance characteristics unmatched by that available through traditional solvent-based coating applications.
Notwithstanding the rapid evolution of water-based coating technology over the last two decades, such coatings have found little acceptance and use in the wood finishing industry. That is due in part to the fact that much effort has gone into developing present finishing schedules utilizing, for the most part, solvent-based coatings. Wood finishing production managers are hesitant to change existing processes which have not only proven to provide consistent product quality but have been developed to do so with optimum cost efficiency. Moreover, the use of water-borne coatings in the wood finishing industry is known by those skilled in this art to have at least one added disadvantage unique for wood finishing applications--water soluble chromophoric (colored) compounds on and in the wood surface bleed through the applied water-based coatings to stain or otherwise blemish the resulting finish. The bleeding of natural occurring tannins, for example, result in staining of applied water-based emulsion paints. Such tannin leachates can also be seen in non-uniformity of color and turbidity in stain-based finishing schedules utilizing water-based finishes. Indeed, it is well-known that the applied stains themselves leach with the natural occurring tannins through after-applied water-based finishes to further distract from finish quality obtainable with water-based coatings.
Yet, in spite of all of the problems presented by use of water-based coatings in the wood finishing industry, proposed state and federal legislation, and promulgation of air quality rules by state and federal agencies may require the wood finishing industry to look to the water-based coating alternatives as a means for reducing its use and release of volatile organic compounds (VOCs).
It is one object of this invention to provide an environmentally sound water-based wood finishing process for obtaining high quality finishes on wood surfaces by eliminating leaching of chromophoric compounds into applied water-based coatings.
It is another object of this invention to provide an improved wood finishing process comprising application of a stain to a wood substrate and subsequent application of at least one water-based coating composition.
In a further embodiment this invention provides a method for reducing volatile organic compounds released in wood finishing processes without sacrificing wood finish quality.
In still another aspect of this invention there is provided a method for preventing discoloration of water-based coatings applied to substrate surfaces due to leaching of chromophoric compounds from the surface into the applied coating.
In one other embodiment there is provided a water-based coating composition comprising anti-leaching effective amounts of a carboxylic acid salt and a water soluble organic compound bearing one or more salt-forming amine groups.
Those and other embodiments of this invention are accomplished by applying to a surface having leachable chromophoric components an effective amount of a carboxylic acid salt and/or a water soluble organic compound bearing one or more salt-forming amine groups and having a molecular weight of about 50 to about 300,000. The amine compound is preferably a monofunctional or polyfunctional amine, or a reaction product of a monofunctional or polyfunctional amine with one or more compounds comprising an amine-reactive functional group, said reaction product having at least one salt forming primary, secondary or tertiary amine group, or acid addition salts of such monofunctional or polyfunctional amines and their said reaction products. The compounds are preferably applied to substrate surfaces in aqueous solution prior to application of the water-based coating. Alternatively the carboxylic acid salt and/or amine compound can be included as a functional component of the water-based coating. Use of the present invention allows reduction, indeed, virtual elimination of usage of volatile organic compounds in commercial wood finishing operations. Water-based coatings can be substituted for traditional solvent-based coatings without loss of the coating quality characteristics of such traditional solvent-based coatings, and with little, if any, added processing costs/time compared to traditional finishing schedules.